(1) Field of the Invention
Swimming pool liners made of polyvinyl chloride (PVC) are subjected to many aggressive factors before and during their period of use. Prior to installation they are folded and stored in cartons. Severe stresses are placed on the PVC liner along the folds of the material in the cartons so that, upon opening, the liners are often found to be cracked.
Once the liners are installed, a multitude of exposures attack the PVC and violate the structural integrity of the polymer. Swimming pool chemicals as well as acidic and alkaline pool liner cleaners contribute to the degrading effects of ultraviolet radiation on the pool liner, especially along the waterline. When the PVC film is subjected to these aggressive agents, degradation of the polymer occurs. The degradation usually manifests itself as a brown stain around the liner above the water line.
(2) Description of the Related Art
Abstract of East German publication 0148-744 of June 1981 to Veb Porzellanw Cold discloses a two component PVC mix with one PVC component having K value of 59-60 while the other has a K value of 66-69. The PVC mix is used for making a mold.
Okano U.S. Pat. No. 4,668,740 of May 26, 1987 mixes PVC with molecular weight in the range of 18,000-43,000 with PVC of higher molecular weight.
Mizutani et al. U.S. Pat. No. 4,267,084 of May 12, 1981 describes mixing a first PVC having a sulfide linkage with a second PVC having a higher molecular weight than the first PVC.
Rhodes et al. U.S. Pat. No. 3,994,844 of Nov. 30, 1976 describes the use of certain zinc organic phosphites as heat stabilizers for vinyl halide resins such as PVC.
Kobayashi et al. U.S. Pat. No. 4,861,816 of Aug. 29, 1989 describes a stabilizer for PVC resins wherein the stabilizer comprises a mixture of barium salts and zinc salts.
Abstract of French 2592-386-A to Soc. Nat. Elf Aquitaine which was published on July 1987 relates to stabilization of halogenovinyl resins against heat by incorporating organic metal compounds and an alkaline earth metal phosphite as stabilizers.
Minagawa et al. U.S. Pat. No. 4,169,089 of Sep. 25, 1979 describes formulations based on various benzophenone compounds which are designed to protect certain polyesters and olefins that are processed at temperatures in excess of 200.degree. C.
Harper et al. U.S. Pat. No. 3,846,395 of Nov. 5, 1974 describes polymeric formulations based on various benzophenone compounds, including p-laurylbenzophenone which are allegedly particularly useful for polyolefin compositions.
M. Isao et al. U.S. Pat. No. 4,659,764 of Apr. 21, 1987 relates to PVC heat stabilizers of barium-zinc carboxylic acid soap mixtures and an organic magnesium compound.
S. Miyata et al. U.S. Pat. No. 4,751,261 of Jun. 14, 1988 relates to PVC stabilizers containing an organic acid salt of zinc.
M. Tadenuma et al. U.S. Pat. No. 5,004,776 of Apr. 2, 1991 relates to PVC heat stabilizers which include alkaline earth metal carboxylates.
Technical Service bulletin of June 1988 of Occidental Chemical Corporation entitled "HIGH MOLECULAR WEIGHT RESI EVALUATION" compares properties of ultra high molecular weight PVC (Oxy 410) in relation to other PVC resins, mentions sheets and gaskets among the uses for such resins and lists advantageous properties.
Witco Material Safety Data Sheet directed to "Mark 4731 LIQUID BARIUM-ZINC STABILIZER", which is a preferred barium zinc-alkyl phosphite used in this invention and which, to applicants, knowledge, has not been used in swimming pool liner formulations.
Customer Service Report No. 87-0047-PAD of Eastman Chemical Products, Inc. which is dated Sep. 8, 1987 and which describes 4-(2-hydroxyethoxy)-2-hydroxybenzophenone as an improved U.V. inhibitor for PVC plastics and which, to applicants' knowledge, has not been used in swimming pool liner formulations.
Pool liner formulations are generally made of a conventional high molecular weight PVC resin such as one having a molecular weight of about 115,000 to 150,000, a conventional benzophenone or benzotriazole ultra violet (UV) absorber and a mixed barium-cadmium-zinc heat stabilizer. Formulation B, shown hereafter, is a prior art formulation.